Define the population of tRNA methyltransferases in normal quiescent, late pregant and lactating mammary gland, and in DMBA-induced mammary tumor. Define the characteristics first in terms of total methyltransferase activity and then analyze the individual methylated neucleosides and the patterns of methylation of the enzymes from the four sources of tissue. After characterizing the methyltransferases, they will attempt to correlate the effects of altered estrogen and prolactin levels on tumor growth with their effects on tRNA methylating activity and tumor specific differences.